I called Arctic Cat today in hopes of speaking with someone. I was transferred to voice mail and left a message. This was at 10:00 this morning. No return call from Arctic Cat was made.

 

I've had a few folks ask me for video of this noise that shows more than just my foot so that they can see exactly what the machine is doing when the noise happens. We made this today out on my rural property using the rear brake only. The rear tires lock up at the end but the noise starts well before they lock up. It also makes the noise (although not nearly as loud) when using the hand brake.

 

From the beginning I've believed this was an unacceptable amount of driveline slack, and I guess I was half right. I spoke with Kent at Arctic Cat. Kent watched the video as well as showed it to in-house technicians at Arctic Cat. According to them, this noise is not only completely acceptable but it is considered normal. He stated that I shouldn't bother returning to the dealership for repairs because there is nothing wrong with my ATV. He also told me that the more I used my rear brake the louder the noise would likely get. He suggested that I shouldn't use the rear brake (what?!?!?) that my machine came with. He also stated that they have three ATVs in their shop and they tested them and that they all do it.
This to me is worse than if the rear end had exploded. A problem in the gear reducer can be repaired, but to accept this level of noise as "normal" is truly a disappointment. That they would allow this level of damage to the machine (the reciprocating axle and all components slapping back and forth) to save the expense of an additional brake caliper makes me wonder what other corners were cut.
Despite this issue I still am happy overall with my ATV. At this point I am seeking a right rear knuckle with caliper that I plan to install on the left rear to get 4 wheel disc. I will update ArcticCatExperience.com to include a tutorial on the process (step by step) that I will create after I finish the upgrade in hopes of helping anyone else who finds this unacceptable.
Thanks to all who helped me out.